thanks a lot. That worked, sorry that I haven't figured that out myself (it's so easy and straightforward).

But after solving this there's another thing I'm currently not able to solve. Let's say I set a new instance of CityDTO as attribute of my old instance of PersonDTO.
My view doesn't get updated. The new instances is in the model but my widgets (in my case a TextField) doesn't update! I'm using DataBindig. Once I save my view and reopen it everything is fine. But I want the widget to update on the fly.
Any Event I need to fire?

What happens in my case:
The attribute innendienstMa of CustomerDTO is getting changed because a new entry in my ComboBox is selected. When the new selection happens I want the mentioned TextField to be updated.